[bug #60589] andoc.tmac: mysterious page number 0a in batch rendering

[G. Branden Robinson]

Update of bug #60589 (project groff):

                  Status:                    None => Fixed                  
             Assigned to:                    None => gbranden               
             Open/Closed:                    Open => Closed                 
         Planned Release:                    None => 1.23.0                 

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Follow-up Comment #3:

Root cause analysis: my paranoid, defensive programming style got me into
trouble.  The semantics of the P and X registers (and only these) were such
that they meant something different when undefined than if they were zero.

groff_mdoc(7) doesn't have use for several of the page rendering options
groff_man(7) does.  In trying to prevent future mdoc development from adapting
these string and register names for incompatible purposes (and making
andoc.tmac's and therefore man(1)'s job much more difficult or impossible), I
made our mdoc implementation assign these entities empty (string) and zero
(register) values, as appropriate, if they were not already defined.

This had bad consequences when switching back and forth between man(7) and
mdoc(7) pages.  When we got back to man from mdoc, P and X looked like they'd
been set to zero by the user.

This had a visible impact only on the last page rendered (and probably only if
that was a man(7) page) because a different bug with footer management meant
that a stale an-page-string could be seen only there.

But I have a fix in the works for that, too, and sorting it out helped me
understand this one.

Now, the only prohibition against adoption of those register and string names
is a cautionary note in our groff_mdoc(7) page.


commit dcdd323bb7ec31ea044674c0a5da50406602276b
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Sat May 15 14:40:37 2021 +1000

    groff_mdoc(7): Re-doc reservation of some names.

commit fba56bcf596b5ad012b5f3a829be7d1b48227bb1
Author: G. Branden Robinson <g.branden.robinson@gmail.com>
Date:   Sat May 15 14:34:39 2021 +1000

    Revert "[mdoc]: Reserve registers used by groff_man(7)."
    
    This reverts commit 8c25d2a1ed2f0046b355b640ed09626c01ac3b7d.
    
    The method I attempted to prevent future squatting on the page rendering
    option name space did not work, and caused problems with some batch man
    page rendering scenarios.
    
    Fixes <https://savannah.gnu.org/bugs/index.php?60589>.


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